Electrophysiological and digital video microscopic techniques are used primarily to elucidate the development, differentiation and cellular distribution of physiological properties expressed by embryonic and postnatal mammalian CNS neurons. Electrical studies involve direct, continuous high-fidelity amplification of ion fluxes generated either in single cells or patches or in pairs of cells in culture. Optical recordings include indirect measurements of membrane potential or conditions (Serum, N3; poly-D-Lysine (PDL), astrocytes) are used as spinal cord neurons differentiate fast-transmitting networks, coculture with astrocytes has immediate and delayed effects. Principal findings activation in a contact-dependent manner in the absence of any changes in unitary channel properties relative to values recorded in neurons on PDL; 2) BAPTA-AM loading of astrocytes eliminates, and coculture in elevated K+ enhances their modulatory effects; 3) coculture immediately enhances voltage-dependent Na+ channel activity relative to that recorded a contact-dependent manner; 4) coculture significantly decreases input resistance and in-creases membrane capacitance after 1 day relative to values recorded in neurons on PDL in a contact-dependent manner; 5) coculture accelerates the time -dependent changes in the Cl- gradient across the plasma membrane and these effects are mimicked by astrocyte- conditioned medium; 6) unitary Cl- conductance increase and open-time spontaneous GABAergic synaptic-like transients appear in progressively more neurons at a faster rate in cocultures and these effects are partially mimicked by astrocyte-conditioned medium; 8) spontaneous glutamatergic synaptic-like transients are also accelerated in their appearance; 9 unitary open-times of GABA-activated Cl- channels estimated in cells dissociated from spinal and supraspinal regions of the embryonic CNS varies and the absolute values correlate with in situ density of specific GABA/A receptor-subunit expressions two-fold; 10) GABA depolarizes gramicidin-perforated-patch-recorded embryonic neurons without triggering action potential activity, yet GABA triggers action CaC2+ elevations in subpopulations of fractionated cortical cells in a similar proportion of cells to that recorded by flow cytometry of suspended cells; 12) GABA, but not muscimol triggers GABAergic Cl- conductance transients at concentrations that do not themselves activate Cl- channels; 13) GABA-induced GABAergic transients are Ca02+dependent. pharmacologically.